Scientists from Climate Central, a research and public outreach organization, suggest natural climate variability along with atmospheric aerosols (that block incoming solar radiation) both play roles in the findings.

For each state in the continental U.S., scientists from Climate Central calculated averages of the daily high and low temperatures from National Climatic Data Center’s U.S. Historical Climatology Network of weather stations. Then, they determined how much the average daily temperatures changed each decade over the past 100 years.

Overall, the scientists found that the pace of warming increased dramatically starting in the 1970s, with every state showing a rise in overall temperatures over the past 40 years. This bump coincides with the time when the effect of greenhouse gases began to overwhelm the other natural and human influences on climate at the global and continental scales, the researchers said.

So they split up their data into two groupings: from 1912 to the present and from 1970 to the present.

Over the past 100 years, the top 10 fastest warming states warmed 60 times faster than the bottom 10 states, or 0.26 degrees F (0.14 degrees C) per decade vs. 0.004 F (0.002 C) per decade.

Since 1970, the speed of warming across the lower 48 states more than tripled, increasing from 0.127 F (0.071 C) per decade over the 100-year period to 0.435 F (0.242 C) per decade since 1970. The gap between the fastest- and slowest-warming states also shrunk after 1970, with the top 10 states heating up twice as fast as the bottom 10 states.

Regional trends were also found, with states in the Southwest, Northeast, Upper Midwest and Northern Rockies showing the fastest warming, while states in the Southeast and Midwest regions tended to warm much slower.

This region of slow warming has been termed "the warming hole" by some; past research showed that aerosol pollutants emitted into the atmosphere over the past 60 years from industrial and power plants in the eastern U.S. would create a cooling pattern similar to this warming hole. Natural climate variability may also play a role in this warming hole, the researchers noted.

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Jeanna Bryner

Before becoming managing editor, Jeanna served as a reporter for Live Science and SPACE.com for about three years. Previously she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a Master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a science journalism degree from New York University.